Magnetoresistive devices use change in the electrical resistance of a material between two electrodes in the presence of a magnetic field to determine the strength of the magnetic field. A certain amount of electrical resistance is present in the material without any magnetic field being applied. When a magnetic field is applied the electrical resistance changes.
The change in the electrical resistance corresponds to the strength of the magnetic field. This change in the electrical resistance is the result of the Lorentz force applied to the charge carrying particles. When a charge carrying particle is in the presence of a magnetic field, the Lorentz force applied to the particle is expressed asF=q[E+(ν×B)],    where F is the Lorentz force in Newtons,    q is the charge of the charge carrying particle in coulombs,    ν is the instantaneous velocity in m/s,    E is the electric field in v/m, and    B is the magnetic field in Tesla. The “×” is the vector cross-product between ν and B.
To ensure proper sensitivity to the magnetic field, it has been a goal of the magnetoresistive device makers in the prior art to maximize the change in the electrical resistance of the magnetoresistive devices when a magnetic field is applied. For example, in semiconductor magnetoresistive devices the mobility of the semiconductor material affects the velocity of the charge carrying particles and thereby affects the Lorentz force applied to those particles. In order to maximize change in resistance, semiconductor materials with high mobilities are often chosen.
The relationship between the change in the resistance in a magnetoresistive device, the applied magnetic field, and the mobility is non-linear. The change in the resistance is proportional to (1+(μB)2), where μ is the mobility. This non-linear relationship presents challenges in determining the direction of the magnetic field when a magnetoresistive device is placed in a magnetic field. For example, the same amount of change in the electrical resistance is experienced whether the magnetic field is coming out of a plane or going into the plane, i.e., positive and negative magnetic fields.
Also, sensitivity to changes in the magnetic field is disadvantageously affected by the non-linear relationship described above. Furthermore, when the magnetic field is parallel to the plane of the magnetoresistive device, change in the electrical resistance is not as easily determinable. This difficulty is due to the vector cross-product of the B field and the velocity of the charge carriers, as provided in the Lorentz force equation. When the magnetic field is parallel to the plane of the magnetoresistive device, the cross product becomes zero since the angle between the two vectors is either 0° or 180°.
Therefore, a need exists to address the stated shortcomings of the prior art. Particularly, a need exists to measure the magnetic field as a result of change in the electrical resistance of a magnetoresistive device with improved sensitivity, including situations where a further need exists for determining the direction of the magnetic field.